This invention includes features of my previous (U.S. Pat. No. 5,598,819) incorporated by reference and describes a design for gasoline piston engines which aims to increase fuel efficiency and reduce CO2 emissions.
4 stroke gasoline engines are relatively fuel efficient at full load but become much less efficient for lower loads when the throttle is partly closed. A previous concept named ‘cylinder de-activation’ allows working cylinders to operate with their throttle fully open when less than full load is needed. For example, if one bank of a V8 engine is de-activated and the other bank operates as a usual 4 stroke engine, with their throttles fully open, this delivers half load.
The present invention causes all cylinders to be de-activated for alternate 4 stroke cycles, when less than half load is needed. The de-activated cylinders of the present invention have ‘air only’ 4 stroke cycles between usual 4 stroke cycles with fuel/air. This enables this engine to deliver half load while the throttles are fully open for the working fuel/air 4 stroke cycles. This is more fuel efficient than half throttling 4 stroke engines or de-activating half the cylinders.
My previous (U.S. Pat. No. 5,598,819) included a camshaft driven at 1:4 crankshaft speed with inlet cams on opposite sides of the camshaft for each cylinder. The fuel/air inlet valve, for one cylinder, opens for a 4 stroke cycle, while the ‘air only’ inlet valve remains closed. For the next 4 stroke cycle, the ‘air only’ inlet valve opens while the fuel/air inlet valve remains closed. This alternate opening inlet valve sequence continues unchanged even when the mode changes from 8 stroke to 4 stroke. A gate valve kept both fuel/air and ‘air only’ inlet ports separate for alternate ‘air only’ cycles and 8 stroke mode. To change to 4 stroke mode for higher power the gate valve, in the ‘air only’ inlet, moves to seal the ‘air only’ inlet and opens a port to the fuel/air inlet to allow fuel/air to enter the cylinder through both inlet valves. The two adjacent 4 stroke cycles are different and become an 8 stroke or Blackburn Cycle for half load or less. The strokes for this cycle are as follows:—1 fuel/air induction, 2 compression, 3 power, 4 exhaust, 5 ‘air only’ induction, 6 ‘air only’ compression, 7 ‘air only’ expansion, 8 ‘air only’ exhaust. If half the maximum 4 stroke load is needed, it follows that power stroke 3 delivers full power and strokes 5-8 deliver no power.
After my previous (U.S. Pat. No. 5,598,819) was filed, tests revealed a disadvantage. The clearance volume in the cylinder head is about 10% of the cylinder capacity and this volume cannot be pushed out of the cylinder by the piston. There is a residue of ‘air only’, after stroke 8, already in the cylinder, which is then mixed with the fresh fuel/air intake during stroke 1 above. If the volume in the inlet pipe between the throttle and the inlet valve seat is also 10% of the cylinder capacity then, even if the throttle is nearly closed, the cylinder is nearly 20% full for the next combustion. This gave too much power and caused a high idling speed.
The present invention replaces the usual throttle valve, located upstream from the inlet valve, with a throttle which is close to the inlet valve when the throttle is nearly closed for idling. A lower power and idling speed can then be achieved reducing the fuel needed. When more than half load is needed from the Blackburn Cycle, fuel is injected for stroke 5 when the 8 stroke cycle becomes two 4 stroke cycles. Other practical design features which were found to be needed during tests are also included in this patent application.